1. Field of the Invention
The invention relates to a process for spraying a liquid intermittently, especially a lubricant suspension to be sprayed under high pressure, by the spray nozzle which automatically opens like an excess pressure valve when the input pressure of the liquid exceeds the threshold value pressure and, when the inlet pressure of the liquid falls short of the threshold value pressure, automatically closes. The invention also relates to a device, for performing the process, having a spray nozzle which automatically opens like an excess pressure valve when the input pressure of the liquid exceeds the threshold value pressure and, when the inlet pressure of the liquid falls short of the threshold value pressure, automatically closes.
2. Background Art
Processes and devices of the type to which the invention relates are used in particular for the lubrication of mandrel rods in the manufacturing of pipes. In this case, as described, e.g., in European Patent Document No. 0192037, a lubricant suspension, especially a high-temperature lubricant suspension basically containing graphite as well as polymers and auxiliary agents, such as, stabilizers, suspended in water (cf. Swiss Published Patent Document Nos. 596,294 and 609,728) is used which is fed to the spray nozzle under very high pressure of, e.g., 50 to 120 bars (even higher in special cases, up to 250 bars) and with flow rates of 20 to 120 m/sec. As the spray nozzle, as indicated in European Patent Document No. 0192037, one is used Which automatically opens like an excess pressure valve when the input pressure of the liquid exceeds a threshold value pressure and, when the inlet pressure of the liquid falls short of the threshold value pressure, automatically closes, is used, as described, e.g., in European Published Patent Application No. 0039839 (FIG. 2).
For spraying the liquid intermittently, a shutoff device placed in front of the spray nozzle is alternately opened and closed. In the case of high pressures and flow rates, the abrasion, which occurs also and especially in the lubricants which are suitable because of the high velocity of the suspended particles (especially the graphite particles), is critical. As explained in detail in European Patent Document No. 0192037, the shutoff devices have therefore been improved in such a way that they can function, on the one hand, despite the high abrasion over a prolonged period and, on the other hand, leaks are recognized in time so that the entire unit does not have to be shut down in the case of a sudden failure of the shutoff device.